GitHub Actions cache isolation lets a run restore caches only from its own
ref or the default branch. Releases run on tag refs and nothing ever ran
on main, so release.yml's rust-cache never restored anything — every
release compiled all 62 crates cold on five targets (~50 min, gated by
Windows at ~49.5 min).
warm-cache.yml builds the same release-dist profile with the same
rust-cache key on main (dep-affecting pushes — including each release's
version-bump commit — plus a weekly refresh against 7-day eviction and
manual dispatch). Tag builds then restore a warm default-branch cache;
the remaining cost is workspace-crate compilation + the codegen-units=1
thin-LTO link, which is the deliberate release-hardening tradeoff.
ZacharyZhang-NY
13ccab980c